The organization of the envelope projections on the surface of HIV.

The organization of envelope projections (knobs) of four different isolates of the human immunodeficiency virus types 1 and 2 (HIV-1 and -2) was studied using surface replica and thin section electron microscopy (EM) in combination with rotational image enhancement. All HIV strains show an identical organization of knobs on the virus envelope. The surface of an "ideal", well-preserved HIV particle is studded with 72 knobs arranged in a T = 7 laevo symmetry. The role of the p 17 protein, which is coating the inner leaflet of the viral envelope, is discussed as a matrix protein functioning as a scaffold for the envelope and its projections during morphogenesis as well as with mature virions.